Redox catalyst oxidant, catalyst and polymerization therewith

ABSTRACT

The invention relates to a method of preparing a composite suitable as an oxidizing component in a redox aqueous emulsion polymerization initiator starting with the relatively harsh oxidation of p-diisopropylbenzene with oxygen and involving a manipulative separation procedure for obtaining the effective oxidizing component. The invention also relates to the oxidizing component, the redox polymerization initiator and to the aqueous emulsion polymerization of selected unsaturated monomers.

This is a continuation of application Ser. No. 784,884, filed Apr. 5,1977, now abandoned.

This invention relates to a diisopropylbenzene hydroperoxide compositesuitable as an oxidant for interaction with a reducing agent, a methodof preparing the composite, and the product thereof as a redox freeradical polymerization initiator. The invention further relates to freeradical polymerizing unsaturated organic compounds in an aqueousemulsion with such a redox initiator or catalyst.

The invention particularly relates to the preparation of the compositefrom a byproduct effluent from a process for producingdiisopropylbenzene dihydroperoxide as an intermediate for producinghydroquinone.

The polymerization of various monomers in an aqueous emulsion is wellknown in the art. Indeed, synthetic rubber latices are convenientlyprepared by the aqueous emulsion free radical polymerization of1,3-butadiene or its copolymerization with other monomers such asstyrene. Such well known emulsion polymerizations are generallyconducted in an aqueous medium in the presence of a surfactant oremulsifier and a free radical initiator or catalyst of the redox typeformed through the interaction between an oxidizing and a reducingagent. The reaction is generally shortstopped at a desired point afterwhich the resultant polymer or copolymer is separated and subjected towashing, filtering and drying operations.

Monohydroperoxide type oxidizing agents for preparation of redoxpolymerization initiators have been widely accepted for use in aqueousemulsion free radical polymerizations. Exemplary are liquid mixtures ofm- and p-diisopropylbenzene monohydroperoxide (U.S. Pat. No. 2,548,435).In practice, it is understood that such a hydroperoxide type initiatorcan be prepared by oxidizing diisopropylbenzene with oxygen underrelatively mild conditions, including the manipulation of temperaturesand/or conversion. The mild preparation conditions such as thecombination of conversions of less than about 25 percent with oxidizingtemperatures below about 100° C. are used in order to preventappreciable formation of both the unwanted dihydroperoxides andoxidation byproducts, such as, for example, phenols, enols and ketones,a portion of which inhibit free radical polymerizations. In practice, itis understood that after the oxidation reaction, the lowmonohydroperoxide concentration is increased to about 50 percent byvacuum distillation of unoxidized hydrocarbon. Thus, the free radicalpolymerization grade hydroperoxide oxidant can be typically obtained ina relatively high purity form in a relatively straight-forward manner.In the mild preparation method, the bulk of the non-oxidant remainder isessentially the simple, unreacted, or unoxidized, diisopropylbenzene.

In contradistinction to the mild oxidation process, the process of moreharshly oxidizing p-diisopropylbenzene to higher conversions is used forthe purpose of preparing the dihydroperoxide for use as a hydroquinoneprecursor. Temperatures in the range of about 110° C. to 120° C. wereused with a conversion to product in excess of 30 percent hydroperoxideequivalent resulting in an appreciable conversion to dihydroperoxide. Amajor portion of the dihydroperoxide was removed by a combination ofcrystallization/precipitation and filtration. The filtrate was a moreconcentrated monohydroperoxide with an attendant more concentratedbyproduct content. The concentrated byproduct content was essentially ofoxygenated compounds.

The remainder composite of monohydroperoxide and concentrated oxygenatedbyproducts was determined to be unsatisfactory for use in a redoxcatalyst for the aqueous emulsion copolymerization of 1,3-butadiene andisoprene.

In practice, the filtrate is recycled to the oxidizing step. In order toreduce byproduct build-up and concentration, a small portion of therecycle stream is purged by vacuum steam distillation with thedistillate being returned to the recycle stream and the byproductrichdistilland, also containing a portion of the monohydroperoxide, removedfrom the system.

The distilland was used as an oxidant for a redox initiator in anaqueous emulsion 1,3-butadiene/styrene polymerization. Althoughcopolymerization occurred, the reaction had an xcessively long inductionperiod, apparently due to residual reaction inhibitors. Thus, thedistilland was found to be inadequate for optimum performance equivalentto the monohydroperoxide oxidant obtained by mildly oxidizingp-diisopropylbenzene.

It is important to appreciate that the induction period is an importantpart of the overall polymerization reaction. The induction period itselfis a period of time preceding the onset of polymerization in which noconversion of monomer is observed and is especially noticeable when thequality of hydroperoxide is not high. Various amounts of inhibitingspecies are apparently formed in the harsh oxidation ofdiisopropylbenzene and subsequent processing, which yields a mixture ofmono- and dihydroperoxides, as well as other oxidation products, one ormore of which is a polymerization inhibitor.

Indeed, it is desired to convert the distilland composite productderived from the more harsh oxidation reaction to an oxidantsubstantially equivalent to the product of the mild oxidation reactionin terms of aqueous emulsion polymerization induction period.

Therefore, it is an object of this invention to provide an efficientoxidant for a redox catalyst from the composite derived from harshlyoxidized p-diisopropylbenzene, a method for its preparation, the redoxcatalyst itself, and the copolymerization therewith of 1,3-butadiene andstyrene.

In accordance with this invention it was discovered that a compositesuitable for use as an oxidizing component in a redox aqueous emulsionpolymerization initiator is a composite prepared by (A) obtaining theoxidiation product of reacting p-diisopropylbenzene with oxygen at atemperature in the range of about 105° C. to about 120° C., preferablyabout 105° C. to about 115° C., said product comprised of a mixture ofp-diisopropylbenzenemonohydroperoxide,p-diisopropylbenzenedihydroperoxide, unreacted p-diisopropylbenzene, andoxygenated byproducts containing aqueous emulsion diene polymerizationinhibitors, (B) removing by a separation procedure, selected from atleast one of crystallization and fractionation followed by subsequentfiltration, a major portion of said p-diisopropylbenzenedihydroperoxide,and treating a portion of the filtrate by fractionation to removep-diisopropylbenzene and a portion of said p-diisopropylbenzenemonohydroperoxide distillate to effect a concentration of the remainderas a distilland having an equivalent monohydroperoxide content by ASTMNo. E-298-68 in the range of about 70 percent to about 90 percentcomprised, by weight of about 45 to about 65, preferably about 50 toabout 60, percent p-diisopropylbenzene monohydroperoxide, about 5 toabout 15, preferably about 5 to about 10, percentp-diisopropylbenzenedihydroperoxide and about 10 to about 30, preferablyabout 15 to about 25, percent oxygenated byproducts, (C) mixing with 100parts by weight of said remainder distilland about 50 to about 400 partsby weight of at least one liquid, non-polar saturated hydrocarboncontaining 5 to about 20, preferably 5 to 10, carbon atoms to form asolid/liquid two-phase product, (D) recovering said liquid phase, (E)treating 100 parts by weight of said liquid phase by mixing therewithabout 50 to about 400 parts by weight of an aqueous sodium or potassiumhydroxide solution containing about 0.5 to about 15 weight percentsodium or potassium hydroxide to form an organic/aqueous two-phaseproduct, (F) recovering said organic phase, (G) treating the recoveredorganic phase one to three times with a dilute aqueous sodium hydroxidesolution containing about 1 to about 4 weight percent sodium hydroxideto form a second organic/aqueous two-phase product and (H) recoveringsaid final organic phase.

In the practice of this invention, it is preferred that in step (A) thep-diisopropylbenzene is oxidized to a sufficient conversion that theproduct has about 40 to about 70 percent hydroperoxide content.

In the practice of this invention it is preferred that in step (B) thefractionation procedure be used whereas the remainder is obtained as adistilland where the fractionation is conducted to a pot temperature inthe range of about 70° C. to about 110° C. In the practice of step (B),as the conversion proceeds, the dihydroperoxide tends to naturallyprecipitate out in the nature of a crystallization. It's removal can beenhanced through filtration.

In the further practice of this invention it is preferred that in step(C) the solid/liquid two-phase product is prepared by mixing saidremainder with the saturated hydrocarbon at a temperature in the rangeof about 15° C. to about 50° C.

Representative of various saturated hydrocarbons for the operation ofstep (C) are paraffin-type hydrocarbons such as n-hexane, isohexane,n-heptane, isoheptane, n-octane and isooctane, and n-decane, as well ascyclic saturated hydrocarbons such as cyclopentane, cyclohexane,cycloheptane and cyclooctane. The paraffin-type saturated hydrocarbonsare preferred of which n-octane is especially preferred for theoperation of this invention. An important feature of step (C) is that anon-polar saturated hydrocarbon is applied to modify the polarity of thesystem so that the subsequent dilute caustic treatment is effective inremoving the aqueous emulsion polymerization inhibitors.

The liquid phase can conveniently be recovered in step (D) byfiltration. In step (E) it is preferred that the treatment is effectedwith adequate mixing of the aqueous caustic and recovered organic liquidphases at a temperature in the range of about 15° C. to about 50° C. andthe system allowed to then equilibrate to an organic/aqueous two-phaseproduct. The organic phase can then be simply withdrawn in step (F) bydraining or decanting.

In the practice of this invention, it is preferred that the organicphase be washed in step (G) one to three more times with the dilutecaustic solution as it was done in step (E) and recovered in step (H) asit was done in step (F) in order to more completely remove aqueousemulsion polymerization inhibitors.

It is important to appreciate in the practice of this invention that theoxidant for the redox catalyst is prepared by first, more harshlyoxidizing p-diisopropylbenzene which forms unwanted byproducts and thenconcentrating such byproducts while refining the overall product toobtain the monohydroperoxide. In the fraction step used for recoveringthe monohydroperoxide, the oxygenated byproducts can be, in part,converted to other forms. At least a portion of the resultingconcentrated byproducts in the monohydroperoxide have been generallyfound to be substantially inhibiting with regard to free radicalformation for aqueous emulsion polymerization. Such byproducts cancontain primarily phenols, enols and ketones, such as at least about 50weight percent and more generally at least about 80 weight percent ofsuch materials. The byproducts can be components attached to one end ofthe p-diisopropylbenzene while a monohydroperoxide constituent isattached to the other end. Alternatively, such components can beattached solely to a p-diisopropylbenzene molecule.

Typically, said byproducts comprise a mixture containing at least twocompounds selected from p-isopropyl acetophenone,2-(4-isopropylphenyl)-2-hydroxyperoxy propane,2-(4-isopropylphenyl)-2-propanol, 1,4-diacetyl benzene,4-(α-methyl-α-hydroxyperoxyethyl)acetophenone,4-(α-methyl-α-hydroxyethyl)acetophenone,1,4-Bis(1-methyl-1-hydroperoxyethyl)benzene,1-(α-methyl-α-hydroxyperoxyethyl)-4-(α-methyl-α-hydroxyethyl)benzene,and 1,4-Bis(1-methyl-1-hydroxyethyl)benzene.

In the preparation of the oxidant portion of the redox catalyst thep-diisopropylbenzene is first preferably oxidized with oxygen to aconversion normally considered to be more favorable to the production ofthe dihydroperoxide and to be excessive for producing good purityp-diisopropylbenzene monohydroperoxide with minimal attendant byproductformation. The product thereof is then treated to remove a major portionof p-diisopropylbenzene dihydroperoxide and unreactedp-diisopropylbenzene as well as a minor portion of themonohydroperoxide. The dihydroperoxide can be substantially removed fromthe product, for example, by conventional crystallization and/orfractionation techniques. The unreacted p-diisopropylbenzene can beremoved by fractionation as a distillate, although a portion of itsmonohydroperoxide will normally be removed also.

As a result in such a fractionation, the normally unwanted byproductsare concentrated as a composite in the monohydroperoxide distilland inthe bottom of the fractionation system.

If the untreated distilland or the alcohol diluted distilland is used asthe oxidant in redox initiated emulsion copolymerization of1,3-butadiene and styrene, an induction period as long as two hours mayoccur.

In the practice of this invention, a free radical aqueous emulsioncopolymerization of 1,3-butadiene and styrene initiated through the useof an oxidant prepared by treating the more harshly derivedmonohydroperoxide composite distilland according to the method of thisinvention had an overall reaction time, without appreciable inductiontime, comparable to such a copolymerization initiated with acommercially obtainable mixture of m- and p-diisopropylbenzenehydroperoxide as the redox catalyst oxidant. Therefore, the treatment ofthe properly refined product made by the more harsh oxidation ofp-diisopropylbenzene was deemed successful in that it demonstrated ahigh grade free radical initiator could be achieved.

The hydroperoxide equivalent concentration can be convenientlydetermined (ASTM No. E-298-68) on the hydroperoxide oxidant composite.By this measure the analysis assumes that all of the hydroperoxide is inthe monohydroperoxide form although it is acknowledged that a portionthereof is dihydroperoxide.

The emulsion polymerization itself is conducted in conventional mannerutilizing conventional emulsifying agents for emulsifying the monomerand product and modifiers such as various mercaptans. The pH of theaqueous phase is conventionally in the range of about 3 to about 12.Conventional reaction times and temperatures are used. The actual redoxcatalyst itself is generated in situ by reacting the oxidant withconventional reducing agents such as ferrous pyrophosphate,hydrosulphite of an alkali metal such as sodium or potassium, sodiumformaldehyde sulphoxylate, various amines such as tetraethylenepentamine and chelated ferrous iron as well as other reducing agentssuch as ferrous sulfate and ferrous chloride.

Various monomers can be polymerized or copolymerized according to thefree radical aqueous emulsion system of this invention such as thosehaving the structure CH₂ ═C<. Representative of such monomers areconjugated dienes such as 1,3-butadiene, 2,3-dimethyl-1,3-butadiene,isoprene, piperylene and chloroprene, and particularly such conjugateddienes in a copolymerization with allyl olefins such as styrene,alpha-methyl styrene, p-chlorostyrene, and the like; acrylic andsubstituted acrylic acids and their esters, nitriles and amides, such asacrylic acid, methacrylic acid; methyl acrylate; ethyl acrylate; andmethyl hexyl acrylate as well as vinyl acetate, vinyl chloride andvinylidene chloride.

Particularly preferable monomers are 1,3-butadiene, styrene andparticularly the combination of butadiene or isoprene with styrene.Usually, in these cases, it is preferred to use relative ratios ofbutadiene to styrene in the range of about 65/35 to about 90/10 byweight.

The practice of this invention is further illustrated by reference tothe following examples which are intended to be representative ratherthan restrictive of the scope of the invention. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

Rubbery copolymers of butadiene and styrene were produced by aqueousemulsion, free radical initiated, polymerization at 10° C. using thefollowing recipe of Table 1:

                  Table 1                                                         ______________________________________                                        Material                     Parts                                            ______________________________________                                        1,3-Butadiene                75.0                                             Styrene                      25.0                                             Tertiary C.sub.12 mercaptan  0.20                                             Water                        200.0                                            Potassium salts of disproportionated rosin acids                                                           2.25                                             Tallow fatty acids           2.09                                             Sodium hydroxide             0.27                                             Sodium salt of condensed naphthalene sulfonate                                                             0.10                                             Trisodium phosphate          0.40                                             Ferrous sulfate heptahydrate 0.04                                             Sulfuric acid                Trace                                            Tetrasodium salt of ethylenediaminetetraacetic acid                                                        0.02                                             Potassium pyrophosphate      0.064                                            Sodium formaldehyde sulfoxylate                                                                            0.024                                            Oxidant.sup.1                0.12                                             ______________________________________                                         .sup.1 Some of the copolymers were made with a hydroperoxide composite        prepared according to the method of this invention and some with a mixtur     of p- and m-diiso-propyl benzene hydroperoxides obtained as DIBHP from th     Hercules Chemical Company containing approximately 50% as                     monohydroperoxide. Slight adjustments in the amounts of oxidants for          slightly varying hydroperoxide contents were made so that equivalent          amounts of oxidants were used.                                           

In the following Table 2 is compared the use of oxidants with inductiontimes and rates of conversion for aqueous emulsion copolymerizations of1,3-butadiene/styrene with a recipe of the type shown in Table 1.

                  Table 2                                                         ______________________________________                                                                     Rate of                                          Oxidant            Induction Conversion                                       ______________________________________                                        A    Distilland.sup.1 diluted with                                                                             after induc-                                      methanol          2 hrs     tion, 10% hr                                 B    Liquid phase.sup.2 from (E) after induc-                                      (filtered solution in octane)                                                                   35 min    tion, 10%/hr                                 C    Organic phase.sup.3 after 2                                                   caustic washes    none      10%/hr                                       D    Commercial oxidant.sup.4                                                                        none      10%/hr                                       ______________________________________                                         .sup.1 Distilland from step (B) described in the specification.               .sup.2 Liquid phase from step (F) described in the specification where th     saturated hydrocarbon used was n-octane in an amount of about 200 parts b     weight per 100 parts by weight distilland.                                    .sup.3 Organic phase from step (H) as described in the specification wher     the saturated hydrocarbon used was n-octane in an amount of about 200         parts by weight per 100 parts by weight distilland and the caustic used       was dilute aqueous sodium hydroxide.                                          .sup.4 Mixture of m- and p-diisopropylbenzene hydroperoxides obtained as      DIBHP from the Hercules Chemical Company.                                

The comparison of oxidant C and D in Table 2 illustrates that theoxidant prepared according to the step-wise method of this invention hasan equivalent performance to the commercially obtained oxidant, whereaswithout the critical recovery steps, the oxidant is inferior, accordingto experiments A and B shown in Table 2.

EXAMPLE 2

A 50-gallon reactor was used to combine 99 pounds of n-octane and 33pounds of distilland obtained from step (B) described in thespecification. The mixture was cooled to 20° C., agitated for 15minutes, and filtered at 18° C. using a 12" deLaval centrifuge. Thefiltrate, 105 pounds, was washed with an equal weight of aqueous twopercent sodium hydroxide and agitated for 15 minutes. After settling for15 minutes, the caustic phase was drained. The wash operation wasrepeated two more times. The organic phase was concentrated bydistilling under a reduced pressure of 26 inches of vacuum at 160° C. orlower. The clear, colorless product, 45% hydroperoxide in octane, wasused to conduct emulsion polymerization using the recipe of Example 1.Polymerization with commercial oxidant, obtained as a mixture of m- andp-diisopropylbenzene hydroperoxide obtained as DIHP from the HerculesChemical Company, was used as control. The polymerization activity, withrespect to onset and rate, was the same for experimental and control.

In the practice of this invention, after the first aqueous caustictreatment of the distilland containing the monohydroperoxide andconcentrated oxygenated byproducts containing emulsion polymerizationinhibitor(s), it is taught to additionally wash the recovered organicphase with dilute caustic. In this regard, it is preferred to wash 100parts by weight recovered organic phase with about 50 to about 400 partsweight of the dilute caustic for each washing operation after theinitial caustic treatment.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A method of preparing a composite suitable as anoxidizing component in a redox aqueous emulsion polymerization initiatorwhich consists essentially of the steps of (A) obtaining the oxidationproduct of reacting p-diisopropylbenzene with oxygen at a temperature inthe range of about 105° C. to about 120° C. to a sufficient conversionthat said product has about 40 to about 70 percent hydroperoxide contentaccording to ASTM No. E-298-68 and is comprised of a mixture ofp-disopropylbenzene mono- and dihydroperoxide, unreactedp-diisopropylbenzene, and oxygenated byproducts containing aqueousemulsion diene polymerization inhibitors, (B) removing by a separationprocedure, selected from at least one of crystallization andfractionation, followed by subsequent filtration, a major portion ofsaid p-diisopropylbenzene dihydroperoxide, and treating a portion of thefiltrate by fractionation to a pot temperature in the range of about 70°C. to about 110° C. to remove p-diisopropylbenzene and a portion of saidp-diisopropylbenzene monohydroperoxide distillate to effect aconcentration of the remainder as a distilland having an equivalentmonohydroperoxide content by ASTM No. E-298-68 in the range of about 70percent to about 90 percent comprised, by weight of about 45 to about 65percent p-diisopropylbenzene monohydroperoxide, about 5 to about 15percent p-diisopropylbenzene dihydroperoxide and about 10 to about 30percent oxygenated byproducts, (C) forming a solid/liquid two-phaseproduct by mixing with 100 parts by weight of said remainder distilland,at a temperature in the range of about 15° C. to about 50° C., about 50to about 400 parts by weight of at least one liquid, non-polar saturatedhydrocarbon selected from at least one of n-hexane, isohexane,n-heptane, isoheptane, n-octane, isoctane, n-decane, cyclopentane,cyclohexane, cycloheptane and cyclooctane (D) recovering said liquidphase by filtration, (E) treating 100 parts by weight of said liquidphase by mixing therewith, at a temperature in the range of about 15° C.to about 50° C., about 50 to about 400 parts by weight aqueous sodium orpotassium hydroxide solution containing about 0.5 to about 15 weightpercent sodium or potassium hydroxide and allowing the mixture toequillibrate to form an organic/aqueous two-phase product, (F)recovering said organic phase by draining or decantation, (G) treating100 parts of the recovered organic phase one to three times with about50 to about 400 parts by weight dilute aqueous sodium hydroxide solutioncontaining about 1 to about 4 weight percent sodium hydroxide to form anorganic/aqueous two-phase product by the method of Step (E) and (H)recovering the final organic phase.
 2. The composite product of claim 1.3. The method of claim 1 where the saturated hydrocarbon used in step(C) is n-octane.
 4. The oxidant composite product of claim
 3. 5. Thefree radical generating redox catalyst suitable for use as an aqueous1,3-butadiene/styrene copolymerization initiator consisting essentiallyof a reducing component and an oxidizing component, where said oxidizingcomponent is a composite prepared according to the method of claim 1 andwhere said reducing component is selected from the group consisting ofat least one of ferrous pyrophosphate, hydrosulphite of an alkali metalselected from sodium or potassium, sodium formaldehyde sulphoxylate,tetraethylene pentamine, chelated ferrous iron, ferrous sulfate andferrous chloride.